Half Marathon Training Plan: 12 Weeks from 10K Fitness to Race Day

You have completed a 10K. You can run for an hour without stopping, you understand pacing, and you know what it feels like to push through discomfort. Now you are ready to make the jump to 13.1 miles, and you need a half marathon training plan built for exactly where you are, not a watered-down beginner programme recycled from a running magazine.

This 12-week plan is written for runners with a 10K base who want a structured, purposeful path to the half marathon finish line. It covers everything from how to calculate your personal pace zones using your current 10K time, to the precise long-run progression that builds your endurance safely to 19 km, to the race-week taper protocol that ensures you arrive on the start line sharp and ready. Whether you are targeting a sub-2:15 or working towards a 2:30 finish, the sessions, pacing guidance, and weekly structure are all here in one place. Follow the plan as written, understand the reasoning behind each phase, and you will cross that finish line healthy and on pace.

Who this plan is for and what you need before week 1

This plan is written for one specific runner: you can cover 10K without stopping, you are running at least three times per week, and you are not currently managing an injury that needs medical attention. If that describes you, you are in the right place. If you are still building toward a continuous 10K, the 8-week plan that takes you from 5K to 10K race day is the better starting point.

Before week 1, check your current weekly mileage. Arriving at this plan with a comfortable base of weekly kilometres already in your legs means the early sessions will feel manageable rather than immediately punishing. Drop below a reasonable floor and the first two weeks carry a real breakdown risk, because the schedule assumes a body that already knows how to absorb consistent running load.

Why 12 weeks is the right block for a 10K-base runner

Twelve weeks is long enough to build the aerobic capacity a half marathon genuinely demands, and short enough to avoid the plateau and accumulated fatigue that plans stretching beyond 18 weeks tend to produce. For a runner at your level, the adaptations you need (a stronger aerobic engine, a long run that reaches 19 km, one quality session per week) happen within this window. Longer does not mean better prepared; it usually means arriving at race day stale.

What this plan is not

This is not a complete beginner programme. It does not start from scratch, and it will not work well if you are still run-walking your kilometres. It is also not a marathon plan with the distance trimmed down. The half marathon has its own demands and its own training logic, distinct from both 10K speed work and marathon endurance accumulation. That distinction shapes every week of the schedule ahead.

One important caveat

If you are managing any pain, returning after a significant break, or have an underlying medical condition, speak to a GP or physiotherapist before starting a structured training block. The guidance here is general training information, not medical advice.

How the 12 weeks are structured: three phases with a purpose

The 12 weeks divide into three phases, each with a distinct job to do.

Phase 1, weeks 1 to 4 (base build). Consistency, not stimulus. You run three times a week plus a long run, all at genuinely easy pace. The long run grows from 10 km to 14 km. There are no quality sessions, deliberately. Adding tempo work before your body has absorbed a reliable weekly rhythm is one of the most common ways an intermediate runner arrives at week 6 with tired legs and a niggling shin.

Phase 2, weeks 5 to 9 (quality build). One structured quality session enters the schedule each week: a tempo run, an interval session, or a progression run. The long run extends toward 18 to 19 km. A step-back week at week 7 drops the long run by 2 to 3 km to let accumulated fatigue clear. The quality session replaces a moderate run; it does not add to the total session count.

Phase 3, weeks 10 to 12 (taper and race). Mileage reduces progressively while short, sharp efforts keep your legs responsive. The goal is to arrive at the start line fresh rather than flat. This phase has its own dedicated section later in this guide.

One quality session per week: a rule, not a compromise

On a three to four day running week, two hard sessions leave insufficient recovery time between stimuli. Inadequate recovery does not produce faster running; it produces injury and flat performances. The second easy run that replaces a potential second hard day is not wasted mileage; it is how the first hard day’s adaptation takes root.

The role of easy running

The majority of running in this plan is genuinely easy, not moderate. Easy pace has a specific meaning here, covered in the next section on pace zones, and it is not the same as shuffling. If you are breathing too hard to hold a conversation, you are not running easy. Runners who treat easy days as moderate days often wonder why their tempo runs feel flat by week 7. These runs build the aerobic base that makes quality sessions productive. The same principle underpins our couch to 5K plan, where aerobic base work does the heavy lifting before any speed is introduced.

Pace zones for this plan: how to calculate yours from a 10K time

Knowing your three phases is only useful if you know what pace to run in each one. “Easy” is not a feeling; it is a number. Running too fast on easy days is the single most common reason intermediate runners arrive at race day tired rather than fresh, so getting these zones right before week 1 matters.

Deriving your zones from a recent 10K time

Take your most recent 10K finish time (run within the last eight weeks, ideally on a flat course). Use the multipliers below to convert your per-kilometre pace into each training zone.

Approximate training-pace multipliers (derived from standard coaching practice, adjust based on feel and heart rate)

Worked examples:

• 55-minute 10K (5:30 min/km): Easy: 6:52 to 7:09 / Long run: 6:36 to 6:52 / Tempo: 5:46 to 5:56
• 60-minute 10K (6:00 min/km): Easy: 7:30 to 7:48 / Long run: 7:12 to 7:30 / Tempo: 6:18 to 6:29
• 65-minute 10K (6:30 min/km): Easy: 8:07 to 8:27 / Long run: 7:48 to 8:07 / Tempo: 6:49 to 7:01

Pace zone table for the sub-2:15 to sub-2:30 range

All paces in min/km.

Notice how far the easy zone sits from race pace: running easy days at 8:50 to 9:10 feels almost embarrassingly slow. That is correct.

When GPS pace is unreliable

On hills, trail surfaces, or into a headwind, use two cross-checks. First, the talk test: easy pace means full sentences without pausing; tempo means short phrases but not a conversation. Second, easy effort feels genuinely conversational; tempo effort allows short phrases but not a flowing conversation, heart rate monitoring can provide a useful cross-check if you use a monitor.

If your 10K time falls outside this range

A 10K under 50 minutes suggests a sub-2:00 half marathon is realistic; over 70 minutes points toward 2:45 or slower. The schedule structure stays the same; only the pace figures change. Use the multiplier table with your actual 10K pace and set a goal reflecting a realistic conversion, most recreational runners find their half marathon pace sits meaningfully slower than their 10K pace per kilometre, so use your actual race result to recalibrate rather than relying on a fixed formula. If your 10K base is still developing, the 9-week beginner running guide on this site will help you build the foundation this plan assumes you already have.

The full 12-week half marathon training schedule

With your pace zones calculated, here is the full schedule. Each week shows session type, target distance, and pace zone, with rest and cross-training days marked.

Pace zones per column: Easy runs and long runs use easy/long-run pace from your zone table. Medium-effort runs sit at the lower edge of tempo pace. Quality sessions vary by week (covered in the next section). Taper weeks retain race-pace efforts to keep the legs responsive.

Weeks 1 to 4: base build

Three easy runs plus one long run each week. No quality sessions. The long run climbs from 10 km to 14 km, adding roughly 1 to 2 km at a time. Every run is easy or long-run pace, building aerobic consistency.

Weeks 5 to 9: quality build

Wednesday becomes your one quality session. Friday moves to a medium-effort run at the lower end of tempo pace. The long run climbs from 15 km to 19 km. Week 7 is a deliberate step-back with the long run dropping to 14 km to clear accumulated fatigue before the push to 19 km. Do not skip this reduction. If a dull ache develops around the knee during this phase, read the Enter2Run guide on runner’s knee: what it is, why it happens, and how to get back running before deciding whether to continue.

Weeks 10 to 12: taper

Weeks 10 to 12 taper progressively, details in the taper section below.

Adapting for 3-day weeks

Keep the quality session and the long run as non-negotiables. Drop the medium-effort Friday run first. Easy run volume falls, but the two core stimuli remain intact.

Cross-training days

Mark cross-training days as recovery, not fitness work. An easy 30 to 45-minute cycle, a low-effort swim, or a light strength circuit supports adaptation without adding fatigue. Keep intensity well below tempo effort.

Quality session formats: what each workout actually looks like

The schedule tells you when to run hard. This section tells you how.

Tempo runs

A tempo run is a sustained effort meaningfully faster than your target race pace but slower than your 10K effort, typically held for around 20 minutes of continuous running, consult the pace-zone table for your specific target. Warm up with 10 minutes at easy pace, run the tempo block, then cool down with 10 minutes easy. The effort should feel “comfortably hard”: you can produce a short sentence, but not hold a conversation. If GPS is unavailable, use that talk-test as your guide. If you can chat freely, push a little; if you cannot speak at all, ease back.

Interval sessions

The following formats are used in this plan as standard coaching practice:

• 6 x 800 m at 10K effort, with 90-second recovery jogs between reps. Each rep should feel hard but controlled. You should finish rep six at roughly the same pace as rep one, not slower. If you are fading badly by rep four, the recovery is too short or the pace is too aggressive.
• 4 x 1,200 m at tempo-plus effort, with 2-minute recovery jogs. Used in the later quality weeks to build sustained speed endurance.

“Hard” in both cases means a 7 to 8 out of 10 effort, not a sprint. You are training the aerobic system, not redlining it.

Progression runs

Start the entire run at easy pace. For the final third, lift to tempo effort gradually. A 9 km progression run means 6 km easy, 3 km tempo. This format is useful if you consistently go out too fast: the enforced easy start removes the decision entirely.

When to back off

Replace a quality session with an easy run if: resting heart rate is notably elevated above your normal morning reading, your legs feel heavy after two easy days, or you are carrying any shin or soft-tissue soreness. On that last point, shin pain in particular warrants prompt attention. If it persists, our guide to shin splints causes, prevention, and return to running is a practical starting point before you consider continuing training.

One quality session per week is a firm ceiling, not a default you should push against. Adding a second hard day is the single most common reason intermediate runners pick up injuries during a half marathon build.

Long-run progression: building to 19 km without breaking down

The long run is the structural spine of this 12-week plan. Everything else, the tempo work, the interval sessions, the easy days, exists to make Saturday’s long run productive and repeatable.

The 10 per cent rule is a starting point, not a ceiling or a mandate. In weeks 1 to 4, increases are deliberately modest, sometimes less than 10 per cent, because a 10K-base runner’s connective tissue and tendons adapt more slowly than cardiovascular fitness does. Adding distance faster than that tissue can absorb is the most reliable route to a stress injury mid-block. Patience in early weeks earns the right to push in weeks 7 to 9.

Distance or time: choose what fits the day. Most weeks, targeting a specific distance keeps progression measurable. On hilly routes or days when accumulated fatigue is evident, switch to time. A 90-minute easy run on rolling terrain is valid long-run stimulus even if the kilometre total is lower than planned. The aerobic work is in the duration, not the number on the GPS screen.

Pace is the point most runners get wrong. Long runs should feel genuinely easy, meaningfully slower than target race pace. Finishing tired but not depleted is the target. If you are breathing hard, you are running too fast. Choosing shoes built for this kind of sustained easy effort matters too, particularly as long-run distances climb past 15 km.

Week 7’s step-back (shown in the schedule above) drops the long run 2 to 3 km to clear accumulated fatigue before the push to 19 km.

The longest run in this plan is 19 km, not 21.1 km. Running the full race distance in training defeats the purpose of taper and leaves your legs carrying unnecessary fatigue to the start line. The remaining distance on race day is covered by reduced training load in the preceding two weeks, race-morning adrenaline, and the pacing discipline this plan has spent 12 weeks building.

Taper and race-week protocol: how to arrive ready

The longest run is behind you. What follows is not the process of more training, it is letting that training surface.

Taper is a deliberate, structured reduction in volume while keeping brief flashes of intensity. It is not two weeks on the sofa. Runners who follow a disciplined taper consistently perform better than those who rest too aggressively or, more commonly, those who cannot resist adding mileage when their legs feel restless.

Weeks 10 and 11: what changes and what stays

In week 10, total weekly mileage drops by roughly 30 per cent. The long run shortens to around 14 km. The quality session stays but reduces: if you have been running 6 x 800 m, bring it to 4 x 800 m. Easy runs stay at their usual pace, just shorter.

Week 11 makes a further significant reduction. The long run is now 10 to 11 km at easy effort. Drop the interval session entirely. One short tempo or progression run of 20 to 25 minutes keeps your legs sharp without accumulating fatigue you cannot shed before Saturday.

Race week, day by day

• Monday: 25 to 30 minutes easy. Settle the nerves, loosen the legs, nothing more.
• Tuesday: Rest or gentle cross-training (light cycling or an easy swim, kept short).
• Wednesday: 10 to 15 minutes at goal race pace inside a 25-minute easy run. Not a workout; a reminder to your legs of what race effort feels like.
• Thursday and Friday: Rest. Completely.
• Saturday or Sunday: Race day.

Taper anxiety is physiological, not informational

Feeling heavy, sluggish, and under-trained in the final ten days is normal. Glycogen stores are topping up, minor muscular inflammation is resolving, and your body is consolidating ten weeks of adaptation. It does not feel like fitness. It is fitness. Do not add mileage. The urge is almost universal and always counterproductive.

Sleep, nutrition, and hydration

Consistent fuelling in the 48 hours before the race matters most. Eat the foods you have trained on, keep portions steady across two or three meals rather than one large carbohydrate hit, and stay consistently hydrated. Carbohydrate loading is not necessary at this distance. Prioritise sleep from Wednesday onwards.

Kit and logistics

Race shoes should be properly broken in, not brand new, but not heavily worn, before the start line. Race kit, including socks and chafing-prevention measures, must have been tested on a long run. Run your race-morning routine at least once beforehand: alarm time, breakfast, travel, warm-up. Surprises on race morning cost time and composure. The night-before guide on the Enter2Run site covers the practical order of preparation in detail.

Arrive at the start line having done less than you think you need. That is the point.

Race-day pacing strategy for a sub-2:15 to 2:30 finish

The taper has done its job. Now you need a plan for the race itself, not just a goal time on a bib.

Stick to even splits, or go fractionally slower early. For an intermediate runner on this schedule, a negative split is the ideal outcome, not the opening strategy. Going out at exactly your target pace and holding it is the most reliable path to a clean finish. Racing the first half on feel almost always means banking time you will pay back with interest after kilometre 16.

The first 5 km is a data-collection phase, nothing more. Race-morning adrenaline will make your target pace feel embarrassingly easy. It is not. Your body is borrowing from reserves it will need later. Treat kilometres 1 to 5 as confirmation that your pacing is correct, not as an invitation to push. If it feels easy, that is the plan working.

Your split targets to write on a card:

• Sub-2:15 target: approximately 6:24 min/km at every kilometre marker (verify with a pace calculator from your goal time)
• Sub-2:30 target: 7:07 min/km at every kilometre marker

Write your splits on a piece of tape on your wrist, or load a pace band before race morning. Check in at km 5, km 10, and the halfway point. A split card removes the mental arithmetic at the moments you can least afford it.

Fuelling follows what you practised in weeks 8 and 9. Take your first gel at the timing you practised in training, and your second in the final third of the race, using the same product and schedule you rehearsed on long runs. If you are relying on race-course drinks, take a small amount at each station from km 8 onwards rather than skipping stations and playing catch-up. If kit comfort is part of your preparation, our guide to the best running shorts for every type of run and every budget covers storage and chafe-prevention so nothing distracts you mid-race.

If you reach halfway ahead of schedule, do not accelerate. Ease back by 5 to 10 seconds per kilometre and return to target pace. A 30-second positive split at halfway costs far less than the collapse that follows trying to sustain a pace your training did not support.

The final 3 km belong to you, if you ran the first 18 conservatively. A disciplined first half leaves genuine energy in reserve. Pick up the pace here, not before. This is where the training pays out.

What comes next: from half marathon fitness to the next goal

Cross the finish line, collect your medal, and then do very little for at least a week. One easy week with no structured running is the minimum before returning to any training schedule. Your legs may feel surprisingly fresh after two or three days, but the muscular and connective-tissue stress from race day runs deeper than that. Resist the urge to plan the next block until that recovery window has closed.

Once you are back, your options depend on what the race showed you.

If you finished sub-2:30 and want to go longer, you already have the aerobic base that a half marathon to marathon training plan needs. Most marathon programmes assume a runner who is already handling a comfortable base of weekly mileage. If this 12-week block brought you to that range, you are not starting from scratch. You are starting with a meaningful head start.

If you want a faster half marathon, use your finishing time rather than your 10K time to recalibrate pace zones before you begin a second cycle. Your half marathon split is a far more accurate predictor of what you are capable of than the 10K time you arrived with twelve weeks ago. A first-time finisher in the 2:25 to 2:30 range who trains specifically for the distance a second time often finds significant time available, particularly if the first race revealed pacing errors.

The pace-zone table earlier in this guide accepts your finishing time as the new input.

Enter2Run’s related guides cover long-run fuelling in detail, pace zone calculation for runners moving into marathon territory, and shoe guidance for the higher weekly mileage a marathon build requires. Use them as the 12-week structure here gave you: one resource at a time, applied to a specific goal.

Ready to start: your 12-week half marathon training plan at a glance

The three-phase structure is set out in full above.

The three rules from the earlier section, easy days genuinely easy, long run protected, one quality session only, apply every week.

If you can cover 10K and you are running three times a week, you have everything this plan requires. You do not need to be fast. You do not need a perfect training history. You need consistency over twelve weeks, and this schedule gives you the exact framework to deliver it.

Your practical next step is straightforward: bookmark the week-by-week schedule table in the section above, open your calendar, and set your week 1 start date. Count back 12 weeks from your race date to confirm the timeline fits. If you have not yet entered a race, do it now. A confirmed entry turns the plan from intention into commitment, and that shift matters more than most runners expect.

The half marathon finish line is a specific, achievable goal for the runner you already are.

Conclusion

Twelve weeks. Three phases. One clear goal.

No special equipment, no elite background, and no guesswork required. Just consistent execution of a plan built specifically for where you are right now.

The runner who finishes a half marathon is the same runner reading this. They just decided to begin.